According to \"Custom Rake Tasks\":
desc \"Pick a random user as the winner\"
task :winner => :environment do
puts \"Winner: #{pick(User).name}\"
end
>
It loads in your Rails environment so you can actually use your models and what not. Otherwise, it has no idea about those things.
So if you made a task that just did puts "HI!" then you don't need to add the :environment task to the dependencies. But if you wish to do something like User.find(1) well that will need it.